1. Field of the Invention
The present invention relates to a phase correction amplifier for correcting a phase characteristic, and a feed-forward amplifier using the above phase correction amplifier, which can be applied to a transmitting power amplifier used, for example, in a radio base station.
2. Description of the Related Art
A power amplifier used for a transmitting apparatus in a mobile radio communication system has a structure in which an amplification is performed within a linear area of an amplification characteristic in order to realize low signal distortion. In this case, however, there is a problem in which this structure has a low power efficiency.
Accordingly, in actual use of the power amplifier, an operation area of the amplification is extended until an output of the power amplifier reaches in the vicinity of a saturation area in order to improve the power efficiency. In this case, when a peak envelope power (i.e., an instantaneous power) of an input signal becomes large, the signal distortion also becomes large.
For example, in a power amplifier used in a PDC (Personal Digital Cellular) system for collectively amplifying and transmitting signals on a plurality of channels, the signal distortion at mutual modulation becomes large compared to amplification of the transmitting signal on a single channel. In a CDMA (Code Division Multiple Access) system, since the peak envelope power becomes large due to coincidence of phases in carrier wave when using large multiplexed codes.
Conventionally, there are known many structures to compensate for the signal distortion in the power amplifier. For example, a pre-distortion type distortion compensator, a feed-forward type amplifier consisting of a distortion extraction loop and a distortion eliminating loop, etc., have been known.
Accordingly, the present invention relates to an improvement of the feed-forward type amplifier by correcting the phase characteristic of a phase correction amplifier.